In the preparation of such products, it is desirable to keep costs to a minimum. It is for this reason that skinless products such as sausages may be preferred to sausages with skins, since the cost applying an edible skin to a sausage can amount to a substantial proportion of the total manufacturing costs. By "skinless" is meant a product free from an external supporting membrane of e.g. collagen or natural gut.
A conventional method of producing skinless products involves the use of a permeable cellulose casing which may be inedible, or at least unacceptable for consumption. This is filled with e.g. meat paste, formed into links, heat processed to form a heat coagulated protein skin and then cooled, after which the cellulose casing is removed. In United Kingdom Pat. No. 1,422,344 there is described a process in which the filled casing is treated with an edible acid which reacts with protein at the surface of the meat paste to form a skin, prior to removal of the casing. This may avoid the necessity for heat processing to provide a coagulated skin, but the disposable casings are relatively expensive and their use is labor intensive.
It has been proposed to prepare a skinless product without the use of casings. One advantageous method of doing this is to treat the surface of e.g. a sausage, after it has been shaped, with a suitable fluid, for example an edible acid which reacts with protein and precipitates to form a cohesive surface for the sausage paste. In U.S. Pat. No. 3,503,756 there is disclosed a process in which a meat emulsion is extruded, and then treated in an acid bath, either before or after cutting into suitable lengths for frankfurters or the like. The treating of the extruded meat does however present handling difficulties.
In United Kingdom Pat. No. 1,441,494 there is disclosed a system in which an edible acid is introduced onto a meat emulsion before it is passed through an extrusion tube, so as to lubricate the emulsion as it passes through the tube, and also to form a cohesive skin for the product as it is extruded. The acid may be introduced through a sintered metal filter.
With this arrangement, as with many extrusion processes, there is the problem of controlling the weight of the product, which must be cut from the extruded length. Moreover, since extrusion and cutting take place after the acid has been introduced, the ends of a product will not be provided with a coagulated skin.
It has been proposed, e.g. in U.S. Pat. No. 2,897,745, to mold a sausage in a rigid re-usable mold. In this arrangement however, it is necessary to cook the product while in the mold, and this may take a considerable time--for example several minutes.
It is known, from for example U.S. Pat. No. 3,940,217, to insert certain treating liquids into a mold prior to injection of the product forming material--in that case a slurry. This does not however ensure an even distribution of the liquid over the product, due for example to gravity effects.